The utilization of networks as a means for fulfilling users' computing needs has increased quite substantially in recent years. Networks, especially those including a central file system shared by the networked computers, offer the advantage over stand-alone personal computers of providing users access to a wide variety of computer resources without consuming large quantities of storage space on the personal computers' local drives. The storage saving advantage is achieved by storing application programs and databases within a shared data storage device connected via a network to a plurality of client computers.
In a network environment, a server is a network entity associated with a resource shared by a network. The server receives requests for the shared network resource from network entities referred to as clients. The server acts upon the requests and issues responses to the clients.
In the example above of a shared data storage device connected to a plurality of clients, a network file server provides clients access to the data on the shared data storage device by receiving requests from the clients for resources provided by the shared data storage device, acting upon the requests, and returning a response to the clients.
One of the problems faced in performing computing tasks in a network environment is the generally longer average wait times for obtaining a response to a request for a resource in comparison to performing the same task locally. After a client transmits a request to a server, a response from the server to the client's request may be delayed because a requested network resource is not currently available. For example, the requested resource may be currently allocated solely to another client in the network, or the computer resource may be unable to respond to any client requests. Other instances in which a client may experience substantial wait times in receiving a response to a request include client requests which require a substantial amount of processing in order to complete. An extended wait time is also incurred for receiving a response to a network request when the request must be routed through a number of heavily traversed routing nodes before reaching its intended destination.
A feature of personal computer operating systems which is gaining popularity as microprocessor speeds and RAM memory capacity increases is the ability to run a plurality of processes simultaneously via time switching the plurality of processes. A personal computer maintains a list of active processes. Each of the simultaneously active processes is executed on the processor for a period of time until the process is interrupted.
In a network environment having clients capable of having a plurality of simultaneously active processes, a process running on the client typically relinquishes its claim to the processor after issuing a network request to a server so that other tasks associated with other active processes may be performed while the process waits for a response to the network request. The processor is then claimed by another one of the plurality of processes. In this environment, more than one of the plurality of simultaneously running processes may attempt to issue a network request to a same network server on a same established virtual circuit (also referred to as a "connection") between the server and the client. A connection refers to a logical conversation established between two computers (in this case a client and a server computer) where each computer maintains state information on the conversation. When developing a communication protocol for a network, one must therefore consider how to handle the situation where a second network request arises in a client computer over a connection for which a first network request is still pending.
In a network environment, it is known for a client and server to coordinate the handling of network requests from client processes in a request and acknowledge mode wherein only a single outstanding request is allowed on a connection between a client and a server. After a client transmits a first request to a server, the client withholds issuing a second request to the server on the connection until a response is received from the server for the first request. Thus, the process from which the second request arises cannot continue until a response is received by the client for the first request.
In known network communication schemes, referred to as "burst" protocols, a client transmits a series of packets of information having a same request sequence number. Each packet within the series of packets is assigned a packet sequence identifier. The "burst" protocol has been used to fragment and then reassemble a virtual packet that, due to restrictions on packet size, cannot be transmitted in a single packet. A fragment list in a response message from the server to the client indicates the ones of the series of packets of information having a same request sequence number that have been successfully received by the server.
The above described multi-packet request protocol for coordinating communications between a client and server does not however permit a second process running on a client to submit a network request to a server on a connection while a first request is pending on the connection until the server has successfully responded to the first request on the connection. The inability of a multi-processing client and a server to support simultaneous multiple outstanding requests on a single client/server connection and to respond to the requests in a different order than the requests were submitted by the client, leads to blocking of the process associated with the second request on the connection.
In other known network communication schemes such as SPX-II, a client submits multiple requests. However, the requests must be processed and replied to in sequence. The known communication protocol resembles a two-way pipeline between a client and server where order is strictly adhered to by the client and the server. This communication scheme does not prevent the blocking of a second network request while a server computes a response to a first network request.